1. Field of the Invention
The present invention relates to a differential pulse code modulation coder and more particularly to such a coder with a greater speed of internal calculation.
2. The Prior Art
The differential pulse code modulation method (DPCM) is often used in connection with the digital transmission and storage of signals. For every current sample s.sub.i, an estimated value is calculated from preceding samples. The difference between the current sample s.sub.i and the estimated value is quantized and subsequently transmitted. This method achieves the advantage of allowing a shorter word length than is required for the representation of the samples s.sub.i. Accordingly, the transmission rate is increased, and the memory capacity requirement is significantly reduced. Given a standard DPCM coder such as described, for example, in FIG. 1 of the German patent OS No. 32 32 516, four arithmetic operations are required within a sampling interval t.sub.A for processing the samples s.sub.i. These arithmetic operations are composed of a subtraction, a quantization, an addition and a multiplication. In the German patent referred to, the internal calculating speed is reduced by the use of the quantizer used, and by a plurality of arithmetic loops.